Draw the shell diagram for the formation of bond between Hydrogen and Nitrogen. Name the compound formed.

Give one importance each of dissolved salts and dissolved gases in water.

(i) List one property in which hydrogen resembles alkali metals and one property in which hydrogen resembles halogens.

(ii) Also list a property in which hydrogen differs from both alkali metals and halogens.

(i) State any one reason for discarding 'Law of Octaves'.

(ii) What is periodicity? Explain the cause of periodicity.